Sidebar: option to group sessions by directory path instead of git remote

Sessions in the sidebar are grouped by git remote URL. Two sibling working directories that share one remote (e.g. projects/BlackSheep and projects/BlackSheep-Level, both pointing at the same BlackSheep.git) collapse into a single group, with the folder name shown only as a prefix on the session title.

Non-git directories already fall back to the folder name, so path-based grouping effectively exists — it just loses to the remote when one is present.

Request: a setting (e.g. sidebarGrouping: "path" | "remote") to prefer the working directory as the group key.

Checked before filing — no existing way to configure this:

• Only sidebarWidth and sidebarVisible exist as sidebar settings.
• sessionGroupingId exists internally but is a remote-control/bridge field, not a display preference.
• claude project only exposes purge.

Environment: v2.x native build, Windows 11.